So I've been studying aging via Markov Chain models that simulate various mutation regimes, trying to get a sense of why our different organ and tissue systems each seem to age at different rates. We know from the pathologists and cancer experts and doctors that, on average, our livers, kidneys and colons begin to accumulate misfolded and unused proteins when we're 20-30 and the accumulation speeds up exponentially when we hit 40. Our brains and hearts, on the other hand, seem to take till about 65 before they really begin showing signs of accumulated damage. They too appear to suffer an exponentially increasing accumulation of damage as well, and this is misfolded proteins, unused proteins, and oxidized mitochondrial free radicals. There is a "mitochondrial free radical" theory of aging which postulates that this IS the major cause of aging, but the models those people have contrived don't accomplish much, which is where my PhD thesis comes in :)
Anyhow, my 2 models finally run in R. The simpler model, a matrix model where the "organism" only has one mutation but must accumulate mutations in order to grow large enough to reproduce, shows a clear trade-off between fitness and mutation accumulation. It seems that if having lots of mutations means you can reproduce a lot, then cancer be damned. In particular if an organism has more kids after it reaches some period of maturity, then the tolerated mutation accumulation rate is much, much higher than an organism that can have an equal number of kids every breeding season.
The second model has 2 organs that can each mutate on their own, or both can in a series basically. So far with that model I don't see the clear tradeoff but I've only just got this massive Markov Chain simulation to run. I'm also doing a thought experiment: I'm asking, "If I observe a given amount of mutations that have accumulated over some period of time, say t, then can I hypothesize about the mutation accumulation rate that that tissue or organ must have experienced over time?" It's an interesting idea because it might allow us to see which organs truly are dissimilar in this sense, and which are not. I'm using some Metropolis-Hastings sims over the next week or two to see how that idea pans out.
Well, my eyes hurt from grading a bunch of freshmen biology quizzes! Night y'all!